COVID-19 can cause mucus and phlegm, and coughing it up is one of the more common ways the illness shows itself in the chest. A dripping nose is less of a COVID hallmark than it is for colds and flu, so the phlegm tends to come from deeper in the airways. The virus also weakens the airway’s built-in system for sweeping mucus out, which is why phlegm can hang on after other symptoms ease.
How Common Phlegm and Runny Nose Are With COVID
About 1 in 3 people with COVID cough up phlegm in the first days of illness.1PubMed Central. Cough and sputum in long COVID are associated with severe acute COVID-19: a Japanese cohort study About half have a cough at onset.2PubMed Central. Cough and sputum in long COVID are associated with severe acute COVID-19: a Japanese cohort study
COVID phlegm is often clear or white. It can feel sticky and hard to cough loose, and it usually comes with a cough that builds over several days. A small amount in the morning is typical, since mucus collects in the airways overnight. Thickness alone doesn’t mean a bacterial infection.
Nose symptoms are less typical. Nasal discharge is noticeably less frequent with COVID than with colds, flu, or sinus infections, where roughly 9 in 10 people have it.3PubMed Central. Comparison of sinonasal symptoms in upper respiratory tract infections during the infectious diseases season of November 2023 to March 2024—a cross-sectional study A stuffy nose affects a little over half of people with COVID, slightly fewer than with colds or flu.4PubMed Central. Comparison of sinonasal symptoms in upper respiratory tract infections during the infectious diseases season of November 2023 to March 2024—a cross-sectional study COVID often starts as a sore throat rather than a dripping nose.5Hina Zaman, MD – Family Care Doctor. COVID vs Flu vs RSV: How to Tell Them Apart and What to Do
Plenty of people get no mucus at all. Many have only a dry cough or no cough, and milder cases may stay in the nose and throat. Having no phlegm doesn’t rule out COVID, so testing still matters.
Many people assume yellow or green phlegm means bacteria and clear means virus. Color mostly reflects immune cells and enzymes passing through the mucus, and that happens in viral illness too. A change to yellow or green is not by itself a reason to ask for antibiotics, which do nothing against the COVID virus and help only if a doctor finds a separate bacterial infection. The pattern matters more than the color: fever returning, breathing getting harder, or feeling worse after improving.
Why COVID Makes Mucus Thick and Hard to Clear
The virus ramps up mucus production. Infected airway cells switch on the genes for the main mucus proteins.6PubMed Central. Prevalence and Mechanisms of Mucus Accumulation in COVID-19 Lung Disease In lab-grown airway tissue, this production peaks about one to two weeks after infection,7PubMed Central. Prevalence and Mechanisms of Mucus Accumulation in COVID-19 Lung Disease so phlegm can get worse in the second week rather than the first.
Inflammation changes the mucus itself. The body’s inflammatory response to the virus triggers extra mucus and changes what it’s made of.8PubMed Central. Cytokine Storm and Mucus Hypersecretion in COVID-19: Review of Mechanisms COVID phlegm tends to be unusually sticky compared with phlegm from other coughs.9American Journal of Respiratory and Critical Care Medicine. Clinical Symptoms and Rheological Characteristics of Sputum in COVID-19-related Cough
The airway’s cleaning system breaks down too. Airways are lined with tiny hairs that beat to push mucus up toward the throat. The virus quickly strips away many of these hairs and weakens the ones that remain.10PubMed Central. SARS-CoV-2 infection induces the dedifferentiation of multiciliated cells and impairs mucociliary clearance These hairs need time to regrow after the virus damages them. Until they recover, coughing does the clearing work, which explains the lingering throat-clearing after you otherwise feel better.
A cough that turns wetter in the second week is not by itself a sign of relapse. Fever and aches often ease first because they come from the early body-wide immune response, while the airway lining is still irritated and repairing. It becomes a concern when the increase comes with new fever, breathlessness, or feeling clearly sicker.
It’s also easy to assume more phlegm means more virus. Volume reflects inflammation and slow clearing, not how contagious you are, and phlegm can rise while the infection is already resolving. How contagious you are is tied more to time since symptoms started than to how much mucus you have.
Mucus is a normal protective coating that traps germs and particles. A productive cough is doing useful work, so strong cough suppression isn’t always the best choice when your cough is wet.
How Long COVID Phlegm Lasts
Most of the recovery happens in the first three months. Phlegm drops from about 1 in 3 people at onset to about 7 in 100 by three months.11PubMed Central. Cough and sputum in long COVID are associated with severe acute COVID-19: a Japanese cohort study It falls only slightly after that, to about 6 in 100 at six months and 5 in 100 at a year.12PubMed Central. Cough and sputum in long COVID are associated with severe acute COVID-19: a Japanese cohort study So if phlegm is still there at three months, it may take much longer to fade.
Lingering cough often comes with phlegm. Among people with a post-COVID cough, meaning a cough lasting weeks after infection, phlegm is the most commonly reported symptom.13PubMed Central. Clinical Characteristics of Post-COVID-19 Persistent Cough in the Omicron Era People with a worse initial illness are more likely to have lingering cough and phlegm.14PubMed Central. Cough and sputum in long COVID are associated with severe acute COVID-19: a Japanese cohort study
A typical course starts with a dry or lightly productive cough along with sore throat, fever, or fatigue. Phlegm often becomes more noticeable in the first couple of weeks, then tapers gradually over the following weeks. A slow, steady decline is reassuring; a sudden return or worsening is not part of normal recovery.
Day-to-day ups and downs are normal. A true setback is a clear change: fever returning, breathing getting harder, or phlegm turning bloody or much heavier along with feeling ill. These can signal a secondary problem such as bacterial pneumonia, so they deserve a medical check rather than waiting it out.
Doctors consider a cough chronic once it passes eight weeks. At that point a visit is worthwhile, and treatments exist for persistent cough.
Who Is More Likely to Have Lasting Mucus
Existing lung and allergy conditions raise the risk. People with COPD, who already tend to build up mucus, may recover more slowly after COVID.15PubMed Central. Post-COVID Respiratory Sequelae in COPD: Mucus Plugging, Infectious Complications, and Risk-Stratified Follow-Up In children, allergies are linked to longer and harsher coughs after COVID, sometimes becoming chronic,16PubMed Central. Cough symptoms in children following COVID-19: a single-center retrospective study because allergic inflammation itself boosts airway mucus.17PubMed Central. Cough symptoms in children following COVID-19: a single-center retrospective study
Severe illness produces very thick secretions. In people in intensive care with COVID, airway secretions can be as thick as those in cystic fibrosis.18PubMed Central. Biochemical, Biophysical, and Immunological Characterization of Respiratory Secretions in Severe SARS-CoV-2 (COVID-19) Infections They soak up water into gel-like tangles that are very hard to cough out.19News Center. Stanford scientists decipher the danger of gummy phlegm in severe COVID-19 That applies to severe hospital cases, not typical illness at home.
If you have asthma or COPD, keep using your regular inhalers during COVID and have a plan with your doctor for flare-ups. Seek care sooner if your breathing worsens.
Smoking already damages the tiny hairs lining the airways and increases mucus. People with chronic bronchitis normally cough up phlegm daily, so it can be hard to tell what’s new from what’s usual. Your own baseline is the useful comparison: more phlegm, a different color, or more breathlessness than usual is worth reporting. Stopping smoking during recovery helps the airway repair, and the benefit begins within weeks.
How to Loosen and Clear COVID Phlegm
Physical techniques move mucus. Breathing techniques, huff coughing, changing position, and gentle movement are all used to help clear COVID phlegm.20PubMed Central. Safety and Efficacy of Chest Physiotherapy in Patients With COVID-19: A Critical Review Devices that make you breathe out against light resistance, including blowing bubbles through a straw in water, are among the options.21PubMed Central. Safety and Efficacy of Chest Physiotherapy in Patients With COVID-19: A Critical Review Staying active and walking can trigger a productive cough.22PubMed Central. Safety and Efficacy of Chest Physiotherapy in Patients With COVID-19: A Critical Review
To huff cough, sit upright and take a medium breath. Breathe out hard through an open mouth, as if fogging a mirror. Repeat two or three times, then cough. It moves mucus with less strain than hacking. At home, drink fluids to keep mucus thinner, use steam or a humidifier, raise your head at night, and avoid smoke.
Medicines have mixed evidence. N-acetylcysteine, a mucus-thinning medicine, has helped in bronchitis,23PubMed. The Potential Mechanism of N-acetylcysteine in Treating COVID-19 but its benefit for COVID is still mostly theoretical.24PubMed Central. N-acetylcysteine for prevention and treatment of COVID-19: Current state of evidence and future directions For post-COVID cough, most people improve within two months whether or not they use a steroid inhaler.25PubMed Central. Clinical characteristics and effects of inhaled corticosteroid in patients with post-COVID-19 chronic cough during the Omicron variant outbreak So a steroid inhaler isn’t routinely needed, though it may help lung function in some people.
Among over-the-counter options, guaifenesin, which is meant to loosen mucus, is widely sold, though evidence that it helps is limited. Cough suppressants can trap phlegm if overused. If you take other medicines, ask a pharmacist before adding anything.
For a stuffy or runny nose, saline sprays or rinses can loosen thick nasal mucus. If you rinse, use distilled, boiled and cooled, or sterile water rather than plain tap water. A warm shower or steam can temporarily open the nose. Blow gently, one nostril at a time, since forceful blowing can push mucus toward the ears and sinuses. Decongestant sprays shouldn’t be used for more than a few days because the stuffiness can rebound.
When Phlegm Is a Warning Sign
Secondary infection is a risk. Extra mucus may fuel inflammation and open the door to a second infection.26PubMed Central. Influence of SARS-CoV-2 on airway mucus production: A review and proposed model In severe COVID, the lungs’ antibacterial defenses can be dampened, allowing bacterial pneumonia.27PubMed Central. Microbial dynamics and pulmonary immune responses in COVID-19 secondary bacterial pneumonia Getting worse after starting to improve deserves a check.
Thick mucus can also block airways. Mucus plugs can limit airflow,28PubMed Central. Cytokine Storm and Mucus Hypersecretion in COVID-19: Review of Mechanisms so shortness of breath matters more than the phlegm itself. Specific red flags are trouble breathing or lips turning bluish, fever returning after days without it, blood in phlegm, and chest pain or confusion.
Phlegm that is rust-colored, pink, or contains blood needs to be reported, especially with fever or chest pain. A sudden big increase in volume combined with feeling clearly worse is more informative than color, and describing that pattern to a clinician helps more than describing the color alone. A visit typically involves listening to your chest, checking your oxygen level, and possibly a chest X-ray.
COVID, Cold, Flu or RSV
Mucus offers some clues. RSV typically causes a wet, chesty cough that worsens later, while COVID’s cough is often dry at first.29Hina Zaman, MD – Family Care Doctor. COVID vs Flu vs RSV: How to Tell Them Apart and What to Do In hospitalized children, nasal discharge was more common with RSV than COVID, 98% vs 73%.30PubMed Central. Comparative Analysis of Symptomatology in Hospitalized Children with RSV, COVID-19, and Influenza Infections Flu tends to start suddenly with high fever and strong body aches,31Hina Zaman, MD – Family Care Doctor. COVID vs Flu vs RSV: How to Tell Them Apart and What to Do while loss of taste or smell points more toward COVID.32Hina Zaman, MD – Family Care Doctor. COVID vs Flu vs RSV: How to Tell Them Apart and What to Do
Colds usually bring a runny nose and sneezing early, with a mild sore throat and little fever. COVID is more likely to include fatigue, body aches, fever, and a cough. These are tendencies, not rules, since newer COVID variants can look very much like a cold. Heavy nasal discharge with facial pain points more toward a sinus infection, which often follows a cold.
Timing offers a little more. Flu often hits within hours, with a sudden high fever and aches, while colds build gradually over a day or two. COVID can start slowly or suddenly, so timing helps less than it does for flu. RSV in adults often looks like a bad cold that moves to the chest after several days.
Because symptoms overlap so heavily, testing still matters. Home tests can confirm COVID, and flu has antiviral treatments that work best when started early.